Method and metal mold for manufacturing optical connector ferrule, optical connector ferrule manufactured by using the method, and optical connector and optical wiring system using the ferrule

ABSTRACT

An optical connector ferrule molding die  1  for molding an optical connector ferrule having a plurality of optical fiber holes comprises an upper die  10,  a lower die  11,  and an intermediate die  12,  whereas the intermediate die  12  comprises a plurality of optical fiber hole forming pins  126  for forming optical fiber holes. The lower die  11  is provided with a protrusion  114  for forming a window hole of the optical connector ferrule, whereas the optical fiber hole forming pins  126  projecting from the intermediate die  12  are secured by through holes  115  penetrating through the protrusion  114  and V-grooves  113.

TECHNICAL FIELD

The present invention relates to a method of making an optical connector ferrule, a die for making the same, an optical connector ferrule made by this method, and an optical connector and optical wiring system using this optical connector ferrule.

BACKGROUND ART

Known as one of optical connector ferrules is an MT (Mechanically Transferable) connector ferrule. This MT connector ferrule has been standardized as IEC60874-16 (1994) and JIS C5981, and comprises a pair of guide holes into which guide pins are inserted and a plurality of fiber holes, disposed between these guide holes, for receiving respective optical fibers.

FIG. 29 shows an example of molding die for molding such an MT connector ferrule. The molding die 60 is constituted by an upper die 69 a, a lower die 69 b, and an intermediate die 65 inserted therebetween. In the intermediate die 65, a pair of planar holding members 65 a, 65 b sandwich and hold therebetween two guide hole forming pins 61 for forming optical connector ferrule guide holes. Held between these guide hole forming pins 61 are a pair of holding members 70 a, 70 b which are thinner and narrower than the holding members 65 a, 65 b. A plurality of optical fiber hole forming pins 63 projecting from distal ends of the holding members 70 a, 70 b so as to form optical fiber holes of an optical connector ferrule are arranged. The inner faces of the upper die 69 a and lower die 69 b are processed so as to form a space corresponding to the outer shape of the optical connector ferrule when all the dies are assembled together, and are further provided with grooves 72, 62 for positioning the respective guide hole forming pins 61, and grooves 64 for positioning the respective optical fiber hole forming pins 63. The lower die 69 b is provided with a protrusion 71 for forming a window frame for the ferrule.

When molding an optical connector ferrule by using such a molding die 60, the intermediate die 65 is initially disposed between the upper die 69 a and lower die 69 b. Specifically, the guide pin forming pins 61 of the intermediate die 65 are placed in the grooves 72 of the upper die 69 a and the grooves 62 of the lower die 69 b, and the optical fiber hole forming pins 63 are arranged in the grooves 64 of the lower die 69 b. Here, as shown in FIG. 31, the holding member 70 b of the intermediate die 65 is held on the protrusion 71 of the lower die 69 b. Then, the space between the upper die 69 a and the lower die 69 b is filled with a molten resin, which is subsequently set and taken out of the die, whereby the optical connector ferrule can be formed.

Thus formed MT connector ferrule is used for connecting optical fibers on an optical transmission line to each other or an optical fiber to an optical member. Here, not only a method in which MT connector ferrules are connected to each other as they are, a method in which the ferrules are provided with housings so as to be formed into connectors for connection has widely been carried out. Widely known as examples of such optical connectors are a connector (generally known as MPX connector) disclosed in Japanese Translated PCT International Patent Application No. 2000-515986A and a multi-fiber connector (generally known as MPO connector) specified in TIA/EIA-604-5-A. When these multi-fiber connectors are used, devices and wiring systems can be made much smaller and denser than those with single-fiber optical connectors. Therefore, backplane wiring, optical interconnected wiring, and the like using these optical connectors as an interface have widely been in use.

DISCLOSURE OF THE INVENTION

The holding members 70 a, 70 b in the intermediate die 65 correspond to a hole for receiving the tape coating of a coated optical fiber tape in the optical fiber connector ferrule formed. The tape coating is so thin that the hole for receiving the tape coating becomes narrow, which makes it necessary to thin the holding members 70 a, 70 b, whereby they are relatively short of rigidity. Therefore, when holding the fiber hole forming pins 63, distal end parts of the holding members 70 a, 70 b may open and yield a gap therebetween as shown in FIGS. 30A and 30B. In this case, when a molten resin is injected during molding, it may enter the gap formed between the holding members 70 a, 70 b and disorder the arrangement of the optical fiber hole forming pins 63. Specifically, as shown in FIG. 31, the resin during molding may enter under the optical fiber hole forming pins 63, whereby the optical fiber hole forming pins 63 may move up while obliquely bending their distal end parts, thus yielding an optical connector ferrule with curved optical fiber holes. In this case, problems such as increases in splice loss may occur when establishing an optical connection by inserting optical fibers into optical fiber holes.

It is an object of the present invention to provide a method of making an optical connector ferrule and a molding die which can improve the accuracy in arrangement of optical fiber holes in an optical connector ferrule molded, an optical connector ferrule made by this method, and an optical connector and optical wiring system using this ferrule.

For achieving the above-mentioned object, the present invention provides a molding die for an optical connector ferrule, the molding die comprising an upper die, a lower die, and an intermediate die disposed therebetween having a plurality of optical fiber hole forming pins, the molding die molding an optical connector ferrule having a plurality of optical fiber holes by injecting and setting a resin therein, wherein the lower die has an inner face provided with a protrusion for forming a window hole at a center part of a body of the optical connector ferrule molded, the protrusion being provided with a through hole for inserting and securing the optical fiber hole forming pins of the intermediate die.

When the optical fiber hole forming pins are inserted through the protrusion for forming the window hole and secured therein as such, deformations of the optical fiber hole forming pins such as bending are suppressed. This improves the accuracy in arrangements of optical fiber holes in the optical connector ferrule made.

The intermediate die is not always inserted in one direction, but may comprise first and second intermediate dies inserted into the lower die in directions opposite from each other. In this case, any of the first and second lower dies may be provided with the optical fiber hole forming pins. Alternatively, the optical fiber hole forming pins may be divided into the first and second intermediate dies and connected/secured between the first and second intermediate dies. This can further improve the accuracy in arrangements.

Preferably, on a connecting end face side of the optical connector ferrule molded, the protrusion is provided with a cutout formed by exposing and opening a part of the peripheral face of the through hole, or a raised part extending along the through hole and having a semicircular cross section with an outer shape increasing as being distanced farther from the connecting end face side. This makes it easier to form a groove connecting with an optical fiber inserting hole.

Preferably, the through hole of the protrusion is arranged so as to shift outward from a center of arrangement positions of the optical fiber hole forming pins at a location corresponding to the connecting end face side of the optical connector ferrule molded. This can suppress the influence of bending of the optical fiber holes during resin molding. Preferably, a line connecting a center of the through hole in the protrusion and a center of a fixing hole on the connecting end face side and a normal from the center of the fixing hole form an angle set to about 0.4 degree or less therebetween.

The present invention includes a method of making an optical connector ferrule using this molding die, and an optical connector ferrule molded by this method.

The optical connector ferrule in accordance with the present invention includes a resin-molded optical connector ferrule comprising a plurality of optical fiber holes arranged therein for receiving and securing respective optical fibers, wherein the optical fiber holes are arranged while being bent such that positions thereof on an inserting end side in a depth of the ferrule are shifted outward from an arrangement center than is the arrangement on the connecting end side. Preferably, the optical fiber hole has a bending angle of 0.2 degree or less at the connecting end face. This can fully reduce the splice loss.

The present invention further includes an optical connector, an optical member, and an optical wiring system which use the foregoing optical connector ferrule.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a first embodiment of the optical connector ferrule molding die in accordance with the present invention;

FIG. 2 is a perspective view showing an example of multi-fiber MT optical connector ferrule molded by using the optical connector ferrule molding die shown in FIG. 1;

FIG. 3 is a sectional view of the molding die in FIG. 1;

FIG. 4 is an exploded perspective view showing a second embodiment of the optical connector ferrule molding die in accordance with the present invention, whereas

FIG. 5 is a sectional view thereof;

FIG. 6 is a perspective view showing an example of multi-fiber MT optical connector ferrule molded by using the optical connector ferrule molding die shown in FIG. 4;

FIG. 7 is an exploded perspective view showing a third embodiment of the optical connector ferrule molding die in accordance with the present invention, whereas

FIG. 8 is a sectional view thereof;

FIG. 9 is an exploded perspective view showing a fourth embodiment of the optical connector ferrule molding die in accordance with the present invention, whereas

FIG. 10 is a sectional view thereof;

FIG. 11 is an exploded perspective view showing a fifth embodiment of the optical connector ferrule molding die in accordance with the present invention, whereas

FIG. 12 is a perspective view showing a protrusion thereof;

FIG. 13 is an exploded perspective view showing a sixth embodiment of the optical connector ferrule molding die in accordance with the present invention, whereas

FIG. 14 is a perspective view showing an optical connector ferrule made by this die;

FIG. 15 is a sectional view showing a seventh embodiment of the optical connector ferrule molding die in accordance with the present invention;

FIG. 16 is a perspective view of an optical connector ferrule made by this die, whereas

FIG. 17 is a sectional view thereof;

FIG. 18 is a perspective view showing a state where optical fiber hole forming pins shown in FIG. 15 are inserted through respective through holes of a protrusion;

FIG. 19 is a perspective view showing the structure of a lower die in FIG. 15 in detail, whereas

FIG. 20 is a perspective view of the protrusion shown in FIG. 15;

FIGS. 21A and 21B are views for explaining arrangements of positioning holes and through holes;

FIG. 22 is a perspective view showing an optical connector using the optical connector ferrule shown in FIGS. 16 and 17;

FIG. 23 is a schematic view showing a state where optical fiber holes are bent in a typical optical connector ferrule;

FIGS. 24A and 24B are views showing a principle by which the bending of optical fiber holes shown in FIG. 23 occurs and a comparison therewith, respectively;

FIG. 25 is a schematic view showing a state where optical fiber holes are bent in the optical connector ferrule shown in FIG. 17;

FIGS. 26 and 27 show experimental data indicating relative bending angles in vertical and horizontal directions at the front end face of an optical connector ferrule;

FIG. 28 is a diagram showing an example of optical wiring system comprising the optical connector shown in FIG. 22;

FIG. 29 is a view showing an example of conventional molding die; and

FIGS. 30A, 30B, and 31 are sectional views showing states where arrangements of optical fiber hole forming pins are disordered when molding an optical connector ferrule by using the conventional molding die.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, preferred embodiments of the present invention will be explained in detail with reference to the accompanying drawings. To facilitate the comprehension of the explanation, the same reference numerals denote the same parts, where possible, throughout the drawings, and a repeated explanation will be omitted.

First Embodiment

FIG. 1 is an exploded perspective view showing a first embodiment 1 of the optical connector ferrule molding die in accordance with the present invention. The optical connector ferrule molding die 1 (hereinafter simply referred to as molding die 1) in accordance with this embodiment is used for molding a multi-fiber MT optical connector ferrule (hereinafter simply referred to as ferrule). FIG. 2 shows the ferrule molded by this molding die 1. The ferrule 2 has two guide holes 21 into which guide pins (not shown) are inserted, whereas four optical fiber holes 22 for receiving respective optical fibers (not shown) exposed from a coated 4-optical-fiber tape are provided. Provided on the rear end side of the optical fiber holes 22 is an optical fiber groove 23 which acts as a guide when inserting the exposed optical fibers into the optical fiber holes 22, thereby making it easier to insert the optical fibers into the optical fiber holes 22 when forming an optical connector. Formed in the upper face part of the ferrule 2 is a window hole 25 for injecting an adhesive.

The molding die 1 is constituted by an upper die 10, a lower die 11, and an intermediate die 12. In the intermediate die 12, four optical fiber hole forming pins 126 forming the optical fiber holes 22 of the ferrule 2 are arranged in a projecting fashion between two guide hole forming pins 125 forming the guide holes 21 of the ferrule 2. The pins 125, 126 are sandwiched and held between a pair of holding members 121, 122, whereas the base end part of the optical fiber hole forming pin 126 disposed at the center is further held between holding members 123, 124 which are thinner than the holding members 121, 122 (and held by the holding members 121, 122). Here, the holding members 121, 122 are secured by screwing, for example. Each optical fiber hole forming pin 126 is constituted by a larger diameter part 126 b located on the base end part side, and a smaller diameter part 126 a disposed at a distal end part of the larger diameter part 126 b. The diameter of the smaller diameter part 126 a is slightly greater than the outer shape of the optical fiber inserted, whereas the accuracy in the position and angle of this part substantially determines the accuracy in the position and angle of the fiber hole in the ferrule molded. It is preferable for the smaller diameter part 126 a to have a length not longer than the minimum length required for securing the angle of the optical fiber inserted, since the fiber inserting characteristic and the strength of molded pins may deteriorate if this part is too long.

As shown in FIG. 3, the upper die 10 and lower die 11 hold the intermediate die 12 therebetween and form a space (cavity) 15 into which a resin is introduced. V-grooves 112 for positioning the respective guide hole forming pins 125 are formed on both end parts of the lower die 11. V-grooves 113 for positioning the respective optical fiber hole forming pins 126 are formed between the V-grooves 112 in the lower die 11 at one end part, whereas a container recess 119 for positioning the holding parts 123, 124 is formed at the other end part.

Disposed at the center of the lower die 11 is a protrusion 114 for forming the window hole 25 of the ferrule 2 for injecting the adhesive. The protrusion 114 is provided with four through holes 115 through which the respective optical fiber hole forming pins 126 are inserted. At the upper end part of the protrusion 114, a cutout 118 is formed on the V-groove 113 side, whereby each through hole 115 is shaped into an U-groove with its upper part opening on the V-groove 113 side. At both end parts of the upper die 10, grooves 101 for pressing and securing the respective guide pins 125 against the lower die 11 are arranged.

When molding the ferrule 2 by using such a molding die 1, the guide hole forming pins 125 and optical fiber hole forming pins 126 are initially held by the holding members 121, 122. Here, the holding parts 123, 124 holding the optical fiber hole forming pins 126 between the guide hole forming pins 125 may be either a member separated from and held by the holding members 121, 122 or a part of an extension of the holding members 121, 122. Subsequently, the guide hole forming pins 125 are placed in the corresponding V-grooves 112 in the state shown in FIG. 1, and the intermediate die 12 is pushed toward the distal ends of the guide hole forming pins 125 and optical fiber hole forming pins 126, so that the optical fiber hole forming pins 126 are inserted through the through holes 115 formed in the protrusion 114 of the lower die 11. Then, the distal end faces (on the side where the optical fiber hole forming pins 126 project) of the holding parts 123, 124 of the intermediate die 12 are brought into contact with the end face of the protrusion 114 on the container recess 119 side, and the distal end parts of the optical fiber hole forming pins 126 are placed in the V-grooves 113. Here, the distal end parts of the guide hole forming pins 125 are placed in their corresponding V-grooves 112 holding the V-grooves 113 therebetween. In this state, the upper die 10 and lower die 11 are closed together as shown in FIG. 3. Preferably, the upper die 10 and lower die 11 are fixed at this time. The intermediate die 12 may be inserted while the upper die 10 and lower die 11 are lightly closed together, and then the upper die 10 and lower die 11 may be fixed.

Then, the space 15 formed by the upper die 10, lower die 11, and intermediate die 12 is filled with a molten resin. As the molten resin, PPS (polyphenylene sulfide) or the like is used, for example. After the resin within the space 15 is set, the upper die 10 and lower die 11 are released from the fixed state, the intermediate die 12 is pulled out, and then the upper die 10 and lower die 11 are opened, whereby the ferrule 2 shown in FIG. 2 is obtained.

In this embodiment, the optical fiber hole forming pins 126 are fixed while being inserted through the through holes 115 formed in the protrusion 114 projecting from the lower die 11, whereby the optical fiber hole forming pins 126 are reliably secured within the space 15. Their securing positions can be made nearer to the distal end face of the optical fiber hole forming pins 126 than conventionally done.

Conventionally, as shown in FIGS. 29 and 31, the base end parts of the forming pins 63 have been held by the holding member 65 movable with respect to the upper and lower dies 69 a, 69 b, whereby their positional relationships with respect to the distal end positioning parts have been hard to determine accurately. In the present invention, the holding parts on the base end part side of the forming pins 126 become the protrusion 114 and thus do not move with respect to the lower die 11. Since the holding parts are always integrated with the lower die 11, it is quite easy to secure the accuracy in arrangements of the base end parts with respect to the distal end positioning parts. This can restrain the optical fiber hole forming pins 126 from bending and deforming when the space 15 is filled with the molten resin at the time of molding the ferrule 2. Namely, the optical fiber hole forming pins 126 are restrained from disordering their arrangement during molding, whereby the occurrence of bending and deformations in the optical fiber holes 22 can be suppressed in the molded ferrule 2. Therefore, the splice loss of optical fibers does not increase when forming an optical connector by inserting optical fibers into the respective optical fiber holes 22 of the ferrule 2 and then establishing an optical connection by butting the end faces of such optical connectors against each other.

In the conventional molding die, the forming pins 63 are secured by simply being held between the holding members 65 a, 65 b at the base end parts, whereby it becomes harder for each forming pin 63 to be held stably by an even force as the number of forming pins 63 is increased by a multi-fiber configuration. As a result, the optical fiber holes tend to deform more. In the present invention, the forming pins 126 are independently inserted into and secured by the through holes 115. Therefore, even when the number of forming pins 126 increases, they can be held as reliably as those in the case where their number is smaller.

In the securing by sandwiching alone, it becomes harder to hold forming pins as their pin diameter is smaller. The present invention uses not only sandwiching but also securing by insertion through the through holes 115, and thus can stably hold the forming pins even when their pin diameter is made smaller. For example, the present invention is suitable for making small-diameter fibers having a cladding diameter of 80 to 100 μm, and connectors including 12 or more fibers such as extra multi-fiber connectors, e.g., one-dimensional 16-fiber connectors, which have come into wider use recently.

In particular, the present invention is suitable for MT connectors known as those of ultra low loss grade. The ultra low loss grade is based on a loss compensation of 0.35 dB in the case of a one-dimensional connector in which optical fibers are arranged in one row, and a loss compensation of 0.5 dB in the case of a two-dimensional connector in which optical fibers are arranged in a plurality of rows. The present invention can stably make an optical connector having such a low loss.

The present invention secures the forming pins 126 by using the protrusion 114 for forming the window hole 24 provided at the center of the body and employed for filling the fiber inserting position with the adhesive in an MT ferrule or the like. The window hole 24 is disposed at substantially the center part of the body, whereby the optical fiber holes 22 can be made accurately. Though the forming pins 126 can be secured at other locations, this is not preferable from the viewpoint of distortions upon shrinkage. Preferably, the forming pins are secured at their larger diameter parts in order to enhance the strength at the securing part.

Since the upper face part of the protrusion 114 is provided with the cutout 118, the optical fiber groove 23 can be formed in front of the optical fiber holes 22 in the molded ferrule 22, which makes it easier to insert optical fibers when forming an optical connector.

When molding the ferrule 2 by the molding die 1, the resin slightly intrudes into the boundary part between the protrusion 114 and the holding parts 123, 124, whereby a projection, i.e., line, is formed by thus intruded resin on the floor 24 of the molded optical connector ferrule 2. Though this line is a slight projection which is negligible in terms of functions of the ferrule, it can easily be distinguished therefrom whether the ferrule 2 is molded by using the molding die 1 of this embodiment or not. Though the ferrule is usable even when the holding parts 123, 124 are not in contact with the protrusion 114, this complicates the inner structure and deteriorates the fiber inserting characteristic, whereby it is usually preferable for them to be in contact with each other.

Second Emodiment

FIGS. 4 and 5 are an exploded perspective view and a sectional view which show a second embodiment 1 a of the molding die in accordance with the present invention. FIG. 6 is a perspective view showing a ferrule 2 a molded by this molding die 1 a.

As shown in FIG. 6, the ferrule 2 a molded by the molding die 1 a of this embodiment is not provided with the optical fiber groove 23 communicating with the optical fiber holes 22 unlike the ferrule 2 shown in FIG. 2. Namely, the floor 24 within the window hole 25 becomes flat. The molding die 1 a of this embodiment is identical to the molding die 1 of the first embodiment in terms of the upper die 10 and intermediate die 12, but differs therefrom in terms of the configuration of the lower die 11 a. The lower die 11 a differs from the lower die 11 of the molding die 1 only in that the protrusion 114 a has no cutout. Namely, the through holes 115 penetrate through the protrusion 114 a.

When such a molding die 1 a is used, the optical fiber holes 22 of the ferrule 2 a shown in FIG. 6 can be made accurately, whereby effects similar to those of the molding die 1, making method, and ferrule of the first embodiment can be obtained.

Third Embodiment

FIG. 7 is an exploded perspective view showing a third embodiment 1 b of the molding die in accordance with the present invention. The greatest difference of the molding die 1 b from the first and second embodiments 1, 1 a lies in that intermediate dies 12 b and 13 b having a separable structure are employed. The ferrule made by this die 1 b is the same as that made by the molding die 1 of the first embodiment, and has the configuration shown in FIG. 2.

The first intermediate die 12 b employs a configuration similar to that of the base end parts of the intermediate dies 12, 12 a of the first and second embodiments. Specifically, a pair of holding members 123, 124 project between two guide pin pipes 127 held by a pair of holding members 121, 122, while having distal end parts holding four forming pin holding pipes 128. Each guide pin pipe 127 has an outer shape in conformity to the base end part of the guide hole forming pin 125 in the intermediate dies 12, 12 a of the first and second embodiments, whereas each forming pin holding pipe 128 has an outer shape in conformity to the larger diameter part 126 b of the base end part of the optical fiber hole forming pin 126 in the intermediate dies 12, 12 a, each being formed like a pipe.

The second intermediate die 13 b has a configuration similar to that of the distal end parts of the intermediate dies 12, 12 a, upper die 10, and lower dies 11, 11 a of the first and second embodiments. Specifically, it has a configuration in which four optical fiber hole forming pins 134 are held between two guide hole forming pins 133 while being sandwiched between a pair of holding members 131, 132. Each guide hole forming pin 133 is secured by a V-groove 135 of the holding member 132 and a groove 137 of the holding member 131, whereas each optical fiber hole forming pin 134 is secured by a V-groove 136 of the holding member 132 and the bottom face of the holding member 132. This structure corresponds to the relationship between the upper die 10 and lower die 11 in FIG. 1.

The upper die 10 b and lower die 11 b basically have respective structures in which the sides of V-grooves 112, 113 are eliminated from the upper die 10 and lower die 11 in FIG. 1.

When molding the ferrule 2 by using the molding die 1 b, the guide pin pipes 127 and forming pin holding pipes 128 are initially held by the holding members 121, 122. Subsequently, the forming pin holding pipes 128 are inserted into their corresponding through holes 115 formed in the protrusion 114 of the lower die 11 b, so as to bring the distal end faces of the holding members 123, 124 into contact with the end face of the protrusion 114 on the container recess 119 side. This places the guide pin pipes 127 into U-grooves 12 of the lower die 11 b. Here, the length (α in FIG. 8) by which the cylindrical part of each forming pin holding pipe 128 on the base end side projects from the protrusion 114 is preferably about 1 mm. When the projection length of the forming pin holding pipes 128 is 1 mm or less, damages to the forming pin holding pipes 128 at the time of manufacture can be reduced more effectively.

Subsequently, the second intermediate die 13 b is inserted into the lower die 11 b so as to oppose the first intermediate die 12 b. Specifically, the guide hole forming pins 133 and optical fiber hole forming pins 134 are inserted into the guide pin pipes 127 and forming pin holding pipes 128, respectively. In this state, the upper die 10 b and lower die 11 b are closed as shown in FIG. 8. The order of assembling the dies is not restricted to the one mentioned above. The second intermediate die 13 b may initially be secured to the lower die 11 b, or the intermediate dies 12 b, 13 b may be inserted after closing the upper die 10 b and lower die 11 b.

Then, a cavity 15 formed within thus assembled molding die 1 b is filled with a molten resin. After the resin within the cavity 15 is set, the intermediate dies 12 b, 13 b are separated from the assembled molding die 1 b, and the upper die 10 a and lower die 10 b are opened. Thus the ferrule 2 shown in FIG. 2 is obtained.

The forming pin holding pipes 128 are supported by the through holes 115 of the protrusion 114 positioned at the center part of the lower die 11 b during molding the ferrule 2 in this embodiment as well, which can restrain the forming pin holding pipes 128 and the optical fiber hole forming pins 134 inserted and supported therein from deforming when filling the cavity 15 with the molten resin, and thus can suppress the disorder in arrangements of the optical fiber holes 22 in the ferrule 2 manufactured. Therefore, the optical fiber connector using this ferrule can achieve a low splice loss. Also, it can lower the stress caused by the resin flow in the forming pin holding pipes 128, thereby reducing damages thereto.

Since the optical fiber hole forming pins 134 are held on the connecting end face side of the ferrule molded, this embodiment can make the ferrule with a high accuracy in optical fiber hole positions at the connecting end face.

Fourth Embodiment

FIG. 9 is an exploded perspective view showing a fourth embodiment of the molding die in accordance with the present invention. This molding die 1 c is used for molding a ferrule having a configuration similar to that of the ferrule 2 shown in FIG. 2. However, the ferrule molded by the molding die 1 c differs from the ferrule shown in FIG. 2 in that each of optical fiber grooves 23 communicating with the respective optical fiber holes 22 is formed with the same diameter as that of each optical fiber hole 22.

As with the molding die 1 b of the third embodiment, the molding die 1 c comprises two intermediate dies 12 c, 13 c. On both sides of an abutment member 129 for forming a coated optical fiber inserting hole at the terminal end part of the ferrule in the intermediate die 12 c, two guide hole forming pins 125 for forming the guide holes 21 of the ferrule are provided, whereas the abutment members 129 and guide hole forming pins 125 are held by a pair of holding members 121, 122.

On the other hand, the second intermediate die 13 c holds four optical fiber hole forming pins 134 inserted in their holding holes, whereas guide hole forming pin holes 138 for receiving the guide hole forming pins 125 held by the first intermediate die 12 c are provided on both sides of the optical fiber hole forming pins 134.

As shown in FIG. 10, the upper die 10 c and lower die 11 c hold therebetween the guide hole forming pins 125 and abutment members 129 of the first intermediate die 12 c and the optical fiber hole forming pins 134 of the second intermediate die 13 c, so as to form a cavity 15 into which a resin is injected. An end part of the lower die 11 c is formed with V-grooves 112 for positioning the respective guide hole forming pins 125.

The inner face of the lower die 11 c is provided with a protrusion 114 for forming a window hole 25 for injecting an adhesive into a ferrule as in other embodiments. The protrusion 114 is provided with four through holes 117 through which the respective fiber hole forming pins 134 are inserted. A cutout 118 is formed on the side where the optical fiber hole forming pins 134 are inserted in the upper end part of the protrusion 114, whereas the through holes 117 in the cutout 118 are formed as U-grooves having an open upper part.

When molding a ferrule by using such a molding die 1 c, the holding members 121, 122 initially hold the guide hole forming pins 125 and abutment members 129, so as to produce the first intermediate die 12 c. Subsequently, the guide hole forming pins 125 are placed in the V-grooves 112 and are advanced until the distal end faces of the abutment members 129 come into contact with the end face of the protrusion 114 on the V-groove 112 side in the lower die 11 c. Then, the second intermediate die 13 c is inserted into the lower die 11 c so as to oppose the first intermediate die 12 c, thereby inserting the optical fiber hole forming pins 134 into the respective through holes 117 provided in the protrusion 114 of the lower die 11 c. Further, the second intermediate die 13 c is inserted into the lower die 11 c, so that the guide hole forming pins 125 are inserted and held in the respective guide hole forming pin holes 138. In this state, the upper die 10 c and lower die 11 c are closed as shown in FIG. 10, so as to assemble the molding die 1 c. Then, the cavity 15 formed within the molding die 1 c is filled with a molten resin. After the resin within the cavity 15 is set, the intermediate dies 12 c, 13 c are slid so as to be separated from the molding die 1 c, and the upper die 10 c and lower die 11 c are opened. This yields a ferrule having a desirable form.

As in the foregoing, the optical fiber hole forming pins 134 are secured and supported by the through holes 117 of the protrusion 114 provided in the lower die 11 c in this embodiment as well. Therefore, even when the cavity 15 is filled with a molten resin, the stress caused by the resin flow in the optical fiber hole forming pins 134 is lowered, whereby their deformations are suppressed. Hence, no disorder in arrangements of the optical fiber hole forming pins 134 occurs, whereby bending and deformations in the optical fiber holes 22 in the ferrule 2 obtained by molding can be suppressed. The optical connector using this ferrule can remarkably lower the splice loss of optical fibers.

Fifth Embodiment

FIG. 11 is a sectional view showing a fifth embodiment of the molding die in accordance with the present invention, whereas FIG. 12 is a perspective view of its protrusion 114 d. The molding die 1 d of this embodiment differs from the molding die 1 c of the fourth embodiment only in that the configuration of the protrusion 114 of the lower die 11 c is modified. The protrusion 114 d of this embodiment is provided with raised parts 119 each having a semicircular cross section in conformity to the optical fiber hole forming pin 134 and extending from the through hole 117 in the inserting direction of the optical fiber hole forming pin 134 (toward the first intermediate die 12 c). The end part of each raised part 119 has an outer peripheral diameter which tapers down toward the opening end of the through hole 117 so as to form a tapered part 119 a toward the opening end. This can make the optical fiber groove 23 in the ferrule 2 wider than the optical fiber hole 22 as shown in FIG. 2 as compared with the case molded by the molding die 1 c of the fourth embodiment, and form the bottom face of the groove 23 with a gradient toward the optical fiber hole 22, thereby making it easier to insert optical fibers.

The first and second embodiments are excellent in the productivity of dies since the intermediate die 12 has a simple form. On the other hand, the third to fifth embodiments are excellent in that they can attain a higher accuracy in fiber positions at the end face. In particular, the third embodiment is excellent in that the length of the smaller diameter parts of the forming pins can be optimized without changing the position of the protrusion. The fourth and fifth embodiments are effective when the fiber holes have such a narrow pitch that a pipe having a sufficiently large outer diameter for receiving a forming pin cannot be placed.

Sixth Embodiment

FIG. 13 is a sectional view showing a sixth embodiment 1 e of the molding die in accordance with the present invention. Though the first to fifth embodiments relate to molding dies which make an optical connector ferrule in which optical fiber holes 22 are arranged in a single row, this molding die 1 e is used for molding an optical connector ferrule 2 e in which optical fiber holes 22 are arranged in two stages as shown in FIG. 14.

This molding die 1 e has a basic configuration identical to that of the molding die 1 c of the fourth embodiment shown in FIGS. 9 and 10. As shown in FIG. 13, the protrusion 114 e disposed on the inner face of the lower die 11 e is provided with two stages of through holes 117 into which respective optical fiber hole forming pins 134 are inserted. On the side where the optical fiber hole forming pins 134 are inserted in the upper end part of the protrusion 114 e, two stages of cutouts 118 are formed. As a consequence, in the cutouts 118, the insertion holes 117 are formed as U-grooves whose upper parts are open.

The method of making a ferrule by the molding die 1 e is identical to that of the fourth embodiment, and yields similar effects. This can accurately make the ferrule 2 e in which the optical fiber holes 22 are arranged in two stages. Thus, the present invention is suitable not only for the molding of an MT ferrule in conformity to a standard, but also for the molding of various ferrules (e.g., two-dimensional 24-fiber ferrules) having a form similar to that of the MT ferrule with its number of fibers different from that of a standard.

Seventh Embodiment

FIG. 15 is a sectional view showing a seventh embodiment of the molding die in accordance with the present invention. This molding die 1 f molds a ferrule such as the one shown in FIGS. 16 and 17.

This ferrule 2 f comprises a pair of guide holes 21 extending from the front end face (connecting end face) 20 toward the rear end and being adapted to receive guide pins (not shown), and a plurality of optical fiber holes 22 (whose number is 24 here) into which optical fibers (see FIG. 21) are inserted. These optical fiber holes 22 are arranged 12 each in two (i.e., upper and lower) stages.

The ferrule 2 has a stepped part 26 therewithin, whereas the upper face part of each step in the stepped part 26 is provided with optical fiber grooves 23 communicating with the respective optical fiber holes 22. The optical fiber grooves 23 act as guide grooves when inserting optical fibers from the rear end side of the optical connector ferrule 2 into the respective optical fiber holes 22 (see FIG. 21), thereby making it easier to insert the optical fibers into the optical fiber holes 22. The upper face part of the optical connector ferrule 2 is formed with a window hole 25 for injecting an adhesive.

When a ferrule molded by using a die having a structure similar to that of the conventional molding die 60 shown in FIG. 29 is used in a case where a plurality of fiber holes are to be provided in a row, the optical fiber holes tend to curve outward more as they are closer to end parts of the arrangement at the front end face (connecting end face) of the optical connector, thereby increasing the splice loss. This embodiment aims at achieving a low splice loss in such a multi-fiber ferrule.

The molding die if has basically the same configuration as that of the molding die 1 of the first embodiment. As shown in FIGS. 15 and 18, the intermediate die 12 f in the molding die 1 f comprises a pair of guide hole forming pins 125 for forming the guide holes 21 of the optical connector ferrule 2, 24 optical fiber hole forming pins 126 for forming the optical fiber holes 22 of the optical connector ferrule 2, holding members 121, 122 for holding the base end side parts of the guide hole forming pins 9, and pin holding parts 123, 124, 129 for collectively holding the base end side parts of the optical fiber hole forming pins 10.

The pin holding parts comprise the upper holding part 123 projecting from the front end face of the upper holding member 121, a lower holding part 124 projecting from the front end face of the lower holding member 122 under the upper holding member 123, and the spacer 129 disposed between the upper holding part 123 and lower holding part 124. The upper holding part 123 and lower holding part 124 are formed with a plurality of V-grooves (not shown) into which base end side parts of the optical fiber hole forming pins 126 are inserted. As a consequence, a plurality of optical fiber hole forming pins 126 are held by the upper holding part 123, the lower holding part 124, and the spacer 129 while in a state arranged in two (i.e., upper and lower) stages.

As shown in FIGS. 15 and 19, the molding die 1 f comprises an upper die 10 f and a lower die 11 f, sandwiching therebetween an intermediate die 12 f holding the optical fiber hole forming pins 126, for forming a cavity 15 having a form in conformity to the optical connector ferrule 2. Both side parts of the lower die 11 f are provided with resin injection gates 119.

The rear end part of the lower die 11 f is provided with two positioning holes 160 into which respective guide hole forming pins 125 of the intermediate die 12 f are inserted. Formed on the inside of the positioning holes 160 is a guide part 161 for introducing the intermediate die 12 f holding the optical fiber hole forming pins 126 into the cavity 15.

The front end part of the lower die 11 f is provided with a pin position determining wall part 150 for positioning the distal end parts of the guide hole forming pins 125 and the distal end parts of the optical fiber hole forming pins 126. The pin positioning wall part 150 has two positioning holes 151 for receiving the respective distal end parts of the guide hole forming pins 125, and a plurality of positioning holes 152, disposed between the positioning holes 151, for receiving the respective distal end parts of the optical fiber hole forming pins 126. These positioning holes 152 are arranged in two (i.e., upper and lower) stages.

Here, the vertical arrangement pitch A of the positioning holes 152, i.e., the distance between the center of the positioning holes 152 on the upper stage side and the center of the positioning holes 152 on the lower stage side (see FIG. 15) is 0.5 mm, for example. The lateral (horizontal) arrangement pitch of the positioning holes 152 is 0.25 mm, for example.

The structure for positioning the distal end parts of the optical fiber hole forming pins 126 is not limited to the above-mentioned pin positioning wall part 150 in particular. For example, a plurality of V-grooves into which the distal end parts of the fiber hole forming pins 126 on the lower stage side are inserted may be disposed on the upper face of the lower die 11 f, a plurality of V-grooves into which the distal end parts of the fiber hole forming pins 126 on the upper stage side are inserted may be disposed on the lower face of the upper die 10 f, and a spacer may be sandwiched between the lower die 11 f and upper die 10 f. In this case, the grooves formed in the lower die 11 f and upper die 10 f and the spacer form a hole part for positioning the distal end parts of the optical fiber hole forming pins 126.

The inner face part of the lower die 11 f is provided with a protrusion 114 f (see FIG. 20) which forms the window hole 25 for injecting an adhesive in the optical connector ferrule 2. The protrusion 114 f is formed with a plurality of through holes 115 into which the respective optical fiber hole forming pins 126 held by the intermediate die 12 f are inserted. These through holes 115 are arranged in two (i.e., upper and lower) stages in conformity to the positioning holes 152 of the pin position determining wall part 150. Also, a stepped part 116 is provided on the front end side of the protrusion 114 f and lower die 11 f. The upper face part of each stage of the stepped part 116 is provided with a plurality of U-grooves communicating with the respective through holes 115.

Here, the arrangement pitch of the through holes 115 differs from that of the positioning holes 152 in the pin positioning wall part 150. FIGS. 21A and 21B are views schematically illustrating this fact. Namely, the positioning holes 152 in the positioning wall part 150 are arranged with uniform pitches A and C in the vertical and lateral directions, respectively. In the protrusion 114 f, by contrast, arrangement pitches are enlarged to A′ and B′ in the vertical and lateral directions, respectively. As a result, the through holes 115 corresponding to the positioning holes 152 are arranged such that the distance from their corresponding positioning holes 152 becomes greater as the through hole 115 is farther from the center.

When molding the ferrule 2 by using this molding die if, the guide hole forming pins 125 of the intermediate die 12 f are passed through the respective positioning holes 160 of the lower die 11 f, and the optical fiber hole forming pins 126 are passed through the respective through holes 115 of the protrusion 114 f as shown in FIG. 18. Subsequently, the intermediate die 12 f is introduced into the lower die 11 f such that the distal end faces of the holding parts 123, 124, 129 abut against the rear end face of the protrusion 114 f, so as to insert the guide hole forming pins 125 and optical fiber hole forming pins 126 into their corresponding positioning holes 151, 152 of the pin positioning wall part 150. In this state, the upper die 10 f and the lower die 11 f are closed as shown in FIG. 15.

Subsequently, a molten resin is injected from the resin injection gates 119 into the cavity 15. Since the optical fiber hole forming pins 126 are inserted through the through holes 115 of the protrusion 114 f here, the optical fiber hole forming pins 126 are restrained from disordering their arrangements.

After the resin within the cavity 15 is set, the upper die 10 f and the lower die 11 f are opened. Then, the intermediate die 12 f is moved to the rear side of the lower die 11 f, so as to pull the guide hole forming pins 125 and optical fiber hole forming pins 126 out of the lower die 1 f. Thus the ferrule 2 f as shown in FIGS. 16 and 17 is obtained.

FIG. 22 is a perspective view showing an optical connector using this ferrule 2 f. The optical connector 50 is formed by inserting optical fibers 52 of two multi-fiber (12-fibers here) coated optical fiber tapes 51 into the optical fiber holes 22 of the optical connector ferrule 2 f from the rear side. The optical fibers 52 are inserted into their corresponding optical fiber holes 22 while in a state where bare optical fibers are exposed by eliminating the coating at their distal end parts, and then are secured with an adhesive.

When establishing an optical connection by using such an optical connector 50, guide pins (not shown) are inserted into the guide holes 21 of the ferrule 2, and then front end faces 20 of such optical connectors 50 are butted against each other as they are. Alternatively, the ferrule 2 f may be provided with a housing so as to form a connector as in MPX and MPO connectors, and then connected to each other.

In the ferrule 2 f molded by the above-mentioned molding die 1 f, the optical fiber holes 22 bend toward each other at their middle part as shown in FIG. 23. This seems be because the space between the optical fiber hole forming pins 126 is so small that the resin is hard to enter there, whereby the resin density in this part becomes lower than that in the surrounding part, thus increasing the shrinkage ratio at the time when the resin sets. When the cavity 15 is filled with the molten resin, the resin initially flows into the side nearer to the ferrule end, whereby the optical fiber hole forming pins 126 receive a pressure directed to the center part of the ferrule. Here, the optical fiber hole forming pins 126 are held at positions to become both end parts of the optical fiber holes, and thus deform so as to flex inward, whereby the optical fiber holes closer to the end sides (outside) deform so as to bend inward more.

As shown in FIG. 24A, when the arrangement pitch of the optical fiber hole forming pins 126 is set identical between the distal end part and base end side of the optical fiber hole forming pins 126 here, the optical fiber holes 21 (corresponding to dotted lines in the drawing) in the front end part of the ferrule 2 (corresponding to the F part in the drawing) bend greater. In this case, the splice loss of optical fibers increases when the front end faces 20 of optical connector ferrules 2 are butted against each other in the state where the optical fibers are inserted in the optical fiber holes 22 so as to establish an optical connection.

In this embodiment, by contrast, the arrangement pitch of the through holes 115 in the protrusion 114f disposed in the inner face part of the lower die 10 f is not fixed but set so as to become greater-than that of the positioning holes 152 of the pin positioning wall part 150 as the through hole 115 is farther from the center in both vertical and lateral directions as shown in FIG. 21B. Therefore, in the optical connector ferrule 2 f molded by the molding die 1 f, the arrangement pitch becomes greater on the rear end side than in the front end part.

When the arrangement pitch of the optical fiber hole forming pins 126 is made greater on the base end side than on the distal end side as such, the distal end parts of optical fiber hole forming pins 126 adjacent each other are bent beforehand in directions opposite from the resin shrinking directions as shown in FIG. 24B. Therefore, even if the adjacent optical fiber holes 22 (corresponding to dotted lines in the drawing) bend (flex) such that their middle parts approach each other when the resin shrinks at the time of molding, bends of the optical fiber holes 22 cancel each other out in the important front end part of the ferrule 2 (corresponding to the F part in the drawing). As a result, the optical fiber holes 22 extend substantially straight toward the rear end of the optical connector ferrule 2 in the front end part of the optical connector ferrule 2 as shown in FIG. 25.

Preferably, in an MT ferrule, the vertical and lateral arrangement pitches of the optical fiber hole forming pins 126 are set greater by about 1 to 10 μm in the base end part than in the distal end part. The pitch range depends on the length of the optical fiber holes 22, whereas the value mentioned above is a preferable range in the case where the optical fiber holes 22 have a length of 3 mm. Preferably, the length of the optical fiber holes 22 is set to the range of about 2 to 5 mm. This is because a length less than 2 mm makes it harder to secure an arrangement accuracy between the base end part and distal end part, increases the window hole 24 too much, and enhances the asymmetry of the ferrule, which may yield a greater molding distortion. On the other hand, a length exceeding 5 mm elongates the span of molding pins, thereby making them easier to deform, and may increase the amount of bending of the pins itself.

Here, the optical fiber holes 22 at the front end face 20 of the optical connector ferrule 2 preferably have a vertical/lateral relative bending angle θ of 0.4° or less. As shown in FIGS. 23 and 25, the relative bending angle θ between the optical fiber holes 22 refers to the angle of intersection between the axes of the optical fiber holes 22 positioned at both ends of the front end face 20 of the optical connector ferrule 2. On the other hand, each optical fiber hole preferably has an angle of emittance δ of 0.2° or less. As shown in FIGS. 23 and 25, the angle of emittance δ refers to the angle of intersection between a normal and the axis of the optical fiber hole 22 at the front end face 20 of the optical connector ferrule 2.

The loss due to such angular deviations can be determined by the following equation of Marcuse:

$T = {\left( \frac{2\omega_{1}\omega_{2}}{\omega_{1}^{2} + \omega_{2}^{2}} \right)^{2}{\exp\left( {{- 2}\frac{\left( {\pi\; n\;\omega_{1}\omega_{2}{\Delta\delta}} \right)^{2}}{\lambda^{2}\left( {\omega_{1}^{2} + \omega_{2}^{2}} \right)}} \right)}}$ where n is the refractive index of the core, λ is the wavelength in vacuum, ω is the mode field diameter=MFD (whose affixes 1 and 2 refer to the exit and entrance sides, respectively), and Δδ is the amount of angular deviation. When a usually employed GeSM optical fiber having an MFD of 4.6 μm is used, the relationship between the angular deviation and splice loss is as summarized in the following table.

angular deviation (°) 0 0.1 0.2 0.3 0.4 0.5 splice loss (d B) 0.0 0.003 0.013 0.030 0.053 0.083

For achieving a splice loss of less than 0.35 dB, which is known as ultra low loss grade, the increase in loss due to the angular deviation is preferably about 0.05 dB or less, for which the angle of emittance δ at the end face of the optical connector is required to be less than 0.2°. The present invention can accurately realize such an angle of emittance δ.

Suppressing the bending of the optical fiber holes 22 at the front end part of the optical connector ferrule 2 as such reduces the splice loss of optical fibers 52 when establishing an optical connection by butting the front end faces 20 of optical connectors 50, each employing such a ferrule, against each other.

Also, as shown in FIG. 25, the distance between the upper and lower optical fiber holes 22 on the rear end side of the ferrule 2 can be expanded without increasing the relative bending angle θ of the optical fiber holes 22 at the front end face 20 of the ferrule 2. Therefore, when inserting the optical fibers 52 of the coated optical fiber tape 51 into the respective optical fiber holes 22 of the ferrule 2 at the time of connection, the upper and lower stages of the optical fiber holes 22 are prevented from being mistaken for each other, whereby the operation time required for connection and the like can be shortened.

FIG. 26 shows experimental data indicating relative vertical bending angles of optical fiber holes at the front end face of an optical connector ferrule. FIG. 27 shows experimental data indicating relative lateral bending angles of optical fiber holes. In FIGS. 26 and 27, black symbols indicate experimental data obtained when vertical/lateral arrangement pitches of the optical fiber hole forming pins are held constant. White symbols indicate experimental data obtained when the arrangement pitches of optical fiber hole forming pins on the base end side are made greater by 8 μm in the case of vertical direction and 2 μm in the case of lateral direction than those in the distal end part. The abscissa of each graph indicates numbers of optical fiber holes in the optical connector ferrule. In FIG. 26, Y₁ to Y₁₂ refer to the optical fiber holes on the lower stage side, whereas Y₁₃ to Y₂₄ refer to the optical fiber holes on the upper stage side. In FIG. 27, X₁ to X₁₂ refer to the optical fiber holes. The ordinate of each graph refers to the angle of inclination with respect to the normal (center axis) of the end face of the optical connector ferrule.

As can be seen from the graphs, when the arrangement pitches of the optical fiber hole forming pins are held constant, the average value P of relative bending angles θ between the upper and lower optical fiber holes is about 0.44°. In the case where the arrangement pitches of the optical fiber hole forming pins on the base end side are made greater than those in the distal end part, on the other hand, the average value Q of relative bending angles θ between the upper and lower optical fiber holes is about 0.15° and thus is improved greatly.

FIG. 28 is a diagram showing an example of optical wiring system comprising the optical connector 50 shown in FIG. 22. In this diagram, the optical wiring system 60 comprises the optical connector 50, and an optical circuit 61 connected to the optical connector 50 via a coated optical fiber tape 51. The optical circuit 61 is constituted by a light-emitting device, a light-receiving device, an optical multi/demultiplexer, an optical branching/combining device, an optical switch, and the like. Thus, the optical wiring system 60 employs the optical connector 50 as an interface, whereas another optical connector 62 is connected to the optical connector 50.

The present invention is not restricted to the above-mentioned embodiments, and modifications combining the embodiments are also included in the scope of the present invention. Though the embodiments in the foregoing explanations are in modes in which the optical fiber holes are arranged in a single row or in two (i.e., upper and lower) stages, the present invention is also applicable to those molding an optical connector ferrule having a plurality of optical fiber holes arranged in three or more stages. The seventh embodiment is favorably applicable to a ferrule in which optical fiber holes are arranged in a single row as well. It is not always necessary for the through holes to be provided one by one. For example, in a configuration in which forming pins are nearly in contact with their adjacent forming pins at larger diameter parts, holes for securing the larger diameter parts are hard to provide one by one, and pins do not shift in the arrangement direction of forming pins even if a hole into which all the forming pins are collectively inserted is provided. In such a case, a continuous hole (having a rectangular or capsule-like cross section) which collectively contains forming pins may be provided. It is important for the present invention to have a configuration which limits the movement of forming pins in directions (vertical and lateral directions) perpendicular to the axial direction in the protrusion.

INDUSTRIAL APPLICABILITY

The present invention is suitable for making an optical fiber connector, and an optical wiring system using this connector. 

1. A molding die for an optical connector ferrule, the molding die comprising an upper die, a lower die, and an intermediate die disposed therebetween having a plurality of optical fiber hole forming pins, the molding die molding an optical connector ferrule having a plurality of optical fiber holes by injecting and setting a resin therein; wherein the lower die has an inner face provided with a protrusion for forming a window hole at a center part of a body of the optical connector ferrule molded, the protrusion being disposed on an inner face of the lower die, the protrusion being provided with at least one through hole for inserting and securing at least one optical fiber hole forming pin of the intermediate die.
 2. A molding die for an optical connector ferrule according to claim 1, wherein the intermediate die comprises first and second intermediate dies inserted into the lower die in respective directions opposite from each other, one of the first and second intermediate dies being provided with the optical fiber hole forming pins.
 3. A molding die for an optical connector ferrule according to claim 1, wherein the intermediate die comprises first and second intermediate dies inserted into the lower die in respective directions opposite from each other, the optical fiber hole forming pins being divided into the first and second intermediate dies and connected/secured between the upper and lower dies.
 4. A molding die for an optical connector ferrule according to one of claims 1 to 3, wherein the protrusion is provided with a cutout exposing and opening a part of a peripheral face of the through hole on a connecting end face side of the optical connector ferrule molded.
 5. A molding die for an optical connector ferrule according to one of claims 1 to 3, wherein, on a connecting end face side of the optical connector ferrule molded, the protrusion is provided with a raised part extending along the through hole and having a semicircular cross section with. an outer shape increasing as being distanced farther from the connecting end face side.
 6. A molding die for an optical connector ferrule according to one of claims 1 to 3, wherein the through hole of the protrusion is arranged so as to shift outward from a center of arrangement positions of the optical fiber hole forming pins at a location corresponding to a connecting end face side of the optical connector ferrule molded.
 7. A molding die for an optical connector ferrule according to claim 6, wherein a line connecting a center of the through hole in the protrusion and a center of a fixing hole on the connecting end face side and a normal from the center of the fixing hole form an angle set to about 0.4 degree or less therebetween.
 8. A method of making an optical connector ferrule, the method arranging an intermediate die having a plurality of optical fiber hole forming pins between upper and lower dies and injecting and setting a resin, so as to mold an optical connector ferrule having a plurality of optical fiber holes, the method comprising the steps of: preparing a lower die comprising a protrusion for forming a window hole at a center part of a body of the optical connector ferrule molded, the protrusion being disposed on an inner face of the lower die, the protrusion being provided with at least one through hole for receiving and securing at least one optical fiber hole forming pin of the intermediate die; and assembling a molding die by inserting the upper and intermediate dies into the lower die; filling a cavity formed within the die with a predetermined resin; and removing the upper and intermediate dies from the lower die after the resin filling the cavity is set, and taking out the molded optical connector ferrule.
 9. A method of making an optical connector ferrule according to claim 8, wherein the intermediate die comprises first and second intermediate dies inserted into the lower die in respective directions opposite from each other, one of the first and second intermediate dies being provided with the optical fiber hole forming pins.
 10. A method of making an optical connector ferrule according to claim 8, wherein the intermediate die comprises first and second intermediate dies inserted into the lower die in respective directions opposite from each other, the optical fiber hole forming pins being divided into the first and second intermediate dies and connected/secured between the upper and lower dies.
 11. A method of making an optical connector ferrule according to one of claims 8 to 10, wherein the optical fiber hole forming pins inserted into the protrusion has a peripheral face partly exposed from the through hole of the protrusion, the exposed part being used for forming a groove part communicating with an optical fiber inserting hole.
 12. A method of making an optical connector ferrule according to one of claims 8 to 10, wherein the protrusion is provided with a raised part extending along the through hole and having a semicircular cross section with an outer shape increasing as being distanced farther from an end face side.
 13. An optical connector ferrule molded by the method of making an optical connector ferrule according to claims 8 to
 10. 14. An optical connector using the optical connector ferrule molded by the method of making an optical connector ferrule according to claims 8 to
 10. 15. An optical member using the optical connector ferrule molded by the method of making an optical connector ferrule according to claims 8 to
 10. 16. An optical wiring system using the optical connector ferrule molded by the method of making an optical connector ferrule according to claims 8 to
 10. 